Open almost any book on grammar or writing skills, and you'll come across the advice
"Use the activevoice in preference
to thepassivevoice".

Also, if you use Microsoft Word, you'll often get similar advice from its grammar
checker.

Free of all the grammatical jargon, what does this mean?

Well, sentences written in theACTIVEvoice have the following structure:

DO-ER ACTION RECEIVER

For example:

John wrote the report.

We misplaced your correspondence.

The council reserved its decision.

The ratepayer thanked him.

As you can see, sentences written in theactive voice all start with the do-er of the action.

Sentences written in thePASSIVEvoice, though, start with the receiver of the action:

RECEIVER ACTION BY-WHOM

For example:

The report was written by John.

Your correspondence was misplaced by us.

The decision was reserved by the Council.

He was thanked by the ratepayer.

Okay, so we've made a distinction between the two. This brings us back to the traditional
advice that it is preferable to write in theactive voice rather than thepassivevoice.

Why?

The reason for this is that theactive voice tends to sound simpler and more direct. Also, it often requires fewer words.

For example:

The dog bit him.[Active]

He was bitten by the dog.[Passive]

We will send your goods within 14 days.[Active]

Your goods will be sent by us within 14 days.[Passive]

Personally, I don't feel that the world is going to end
if you write a few sentences in the passive
voice now and then. Nonetheless, using theactive voice in the majority of cases will improve your writing by making it simpler and more direct.

The passive voice does have one "advantage" though: it allows us leave out the do-er. Consider this alternative structure
forpassivesentences:

RECEIVER ACTION

For example:

The report was written.[By whom?]

Your correspondence was misplaced.[By whom?]

The decision was reserved.[By whom?]

He was thanked.[By whom?]

By leaving out the do-er, thepassive voice allows us to hide responsibility. It is thus much loved in government reports. :-)

When we write in theactivevoice, though, we are forced to identify the do-er, and this eliminates a certain amount of evasion.